Usually a systolic blood pressure reading below 90 mm of Hg or a diastolic blood pressure reading below 60 mm of Hg is considered a low blood pressure or hypotension. Some people may normally have a low blood pressure, especially if they do regular exercises. Presence of symptoms is more important than just a low blood pressure reading. Symptoms signify inadequate supply of oxygen to vital organs like brain and heart. If there is no underlying condition causing it and the person is not having any symptoms, no therapy is indicated for low blood pressure.
Low blood pressure can be caused by numerous conditions. Some of the most commonly encountered ones are dehydration, heart disease, acute blood loss, pregnancy, shock, anti-hypertensive drugs and endocrine diseases.
Shocks (various types)
There is another somewhat different type of low blood pressure condition known as orthostatic hypotension or postural hypotension. In this, the low blood pressure is temporary and the blood pressure falls only when the person is standing up from a lying down or sitting position. This sudden fall in blood pressure may cause dizziness or even fainting. Similarly, there is postprandial hypotension, in which the blood pressure falls after a meal. The fall in blood pressure may give rise to symptoms of low blood pressure. Both of these conditions are more common in old age.
General approach to management of low blood pressure is first an evaluation for an underlying cause. Treatment is given only if there are symptoms or the underlying condition is associated with increased risk of complications in the future. Asymptomatic low blood pressure with no underlying serious cause requires no treatment. As already mentioned, any type of shock is a serious life-threatening emergency and requires immediate medical care.